This book examines the tsunami phenomenon with the focus on its relevance for hazard assessment at nuclear power plant sites. Three tsunamigenic mechanisms (earthquakes, landslides, and volcanoes) are considered. Also discussed are offshore and onshore modelling of tsunami waves and their effects on nuclear power plant structures, systems, and components. Identification of the repository of historic tsunami data and ways to approach site safety assessment for tsunamis by a Nuclear Regulatory Commission is also reviewed.